1. Field of the Invention
The present invention relates to a pickup driving device for a disk player for playing an information recording disk.
2. Description of the Related Art
An example of a conventional pickup driving device will be explained referring to FIG. 1.
As shown in FIG. 1, a control circuit 1 for a disk player comprises a microprocessor (hereinafter referred to as MPU), a memory, etc. The control circuit 1 controls the operation of a motor for driving a slider, not shown in the drawing, which moves freely in the radial direction of a disk while holding a pickup for reading a signal recorded on an information recording disk such as a video disk. The control circuit 1 supplies an FWD signal when the slider is to be moved in the forward direction and an REV signal when it is to be moved in the reverse direction to a voltage generator circuit 2. The voltage generator circuit 2 comprises an operational amplifier OP1 and resistors R21 to R24; the FWD signal is input to a negative-phase input terminal of the operational amplifier OP1, and the REV signal is input to a positive-phase input terminal of the operational amplifier OP1. Usually only one signal, an FWD signal or an REV signal, is generated. When a FWD signal is supplied to the operation amplifier OP1, it generates a negative voltage signal to make the motor generate a driving force in the forward direction; when a REV signal is supplied to it, it generates a positive voltage signal to make the motor generate a driving force in the reverse direction. The level of the voltage signal is decided by the amplitude or the pulse width of the FWD signal or the REV signal. The voltage signal is supplied to an output amplifier circuit 3 comprising an operational amplifier OP2 and resistors R31 to R32. The power amplifier circuit 3 power-amplifies the voltage signal and supplies it to a driving coil 4 of a linear motor etc. The driving coil 4 generates an electromagnetic force corresponding to the polarity and the level of a supplied current to energize a slider in a positive or negative radial direction.
A magnetic circuit, not shown in the drawing, is disposed along the moving path of the slider, and a speed detection coil 5 is provided for the slider to be in the proximity of the magnetic circuit. When the slider is moved by the motor, the speed detection coil 5 intersects magnetic flux and generates an electromotive force of a level corresponding to the speed of the slider. The electromotive force is supplied to an equalizer amplifier 7 through a buffer amplifier 6.
The equalizer amplifier 7 comprises an operational amplifier OP3, resistors R71 to R73, and capacitors C71 and C72; it reverse-amplifies the output of the speed detection coil 5 with a characteristic to compensate the moving speed versus output characteristic of the speed detection coil 5. The output of the equalizer amplifier 7 is supplied to a negative input terminal of the power amplifier circuit 3 through the resistor 32. The speed detection coil 5, the buffer amplifier 6 and the equalizing amplifier 7 constitute a negative feedback circuit.
The above-mentioned negative feedback circuit functions to suppress the influence of external disturbances and to increase the stability of a slider servo system during a disk is played.
In the constitution as described in the above, when a search command or a DC component of a tracking error signal from a tracking servo system, not shown in the drawing, is applied to the control circuit 1, the control circuit 1 outputs a FWD signal or a REV signal to operate a slider motor. The driving coil 4 of the motor energizes the slider in the positive direction during a FWD signal is being generated, and it energizes the slider in the negative direction during a REV signal is being generated.
In this manner, the slider is moved in the radial direction of a disk so that a pickup can be disposed at a desired read position. The present applicant proposed several high speed search methods for a target address in a disk player in a Japanese patent, laid-open No. 224964/87.
An example of the above-mentioned high speed search methods will be explained referring to FIG. 2.
FIG. 2 shows an operation chart of a method introduced as a high-scan subroutine. This method is suited to the case where a present address and a target address are apart by more than 3000 tracks. When a search command is given to a control circuit, the MPU decides the execution of the high-scan subroutine judging from the difference between a present address and a target address on a disk being played, and executes a control operation in a acceleration region (M1). A full power is supplied to the driving coil 4 of the motor for driving a slider; the slider is accelerated toward a target address. When a number of track lines crossed by an information reading point exceeds a predetermined number, the MPU executes a control operation in a deceleration region (M2) applying brakes on the motor. When a number of tracks till a target track becomes less than a first value the MPU moves to a control operation of a constant speed movement mode (M4) in which the slider is moved at a constant speed, through a constant speed servo pull-in control mode (M3).
For example, there are two kinds of speed servo control modes, 54 and 36 kilotracks/sec in a constant speed servo pull-in control mode (M3). In a deceleration region, when a remaining number of tracks becomes smaller than a first value or the slider speed becomes lower than 80 kilotracks/sec, the 54 kilotracks/sec speed servo control is executed which acts to control the track-crossing speed of an information reading point to be maintained at 54 kilotracks/sec, and when the remaining number of tracks becomes smaller than a second value, the 36 kilotracks/sec speed servo control is executed which acts to control the track-crossing speed of an information reading point to be maintained at 36 kilotracks/sec. When the remaining number of tracks becomes smaller than a third value a constant speed movement servo control (M4) is executed. As mentioned in the above, it is made possible to smoothly proceed from a deceleration region (M2) to a constant speed movement region (M4) by utilizing the speed servo controls as mentioned in the above.
When the number of remaining tracks reaches a fourth value, a tracking servo control (M5) is started; a frame number is read and a correct address of the present position of an information reading point is detected (M6). A compensation multijump (M7) control or a single-jump control (M9) is selected based on the difference between the present address and a target address. After a compensation multijump control is executed, the tracking servo control is started again and the frame number is read (M8) and a number of compensation single jumps (M9) corresponding to the number of remaining tracks are repeated till a target address is reached.
In the case of a disk player in which the high scan subroutine is executed, a slider can move at a high speed; therefore such a disk player has a merit that it can finish a search operation in a short time even when the present address and the target address of the slider are much apart from each other.
On the other hand as mentioned in the above, a pickup driving device has a negative feedback circuit. In the negative feedback circuit, the higher becomes the movement speed of a slider the more increases the negative feedback quantity. Because of this, even though the control circuit gives a command of full power, the increase of the speed of a slider is suppressed after the slider speed reaches a certain level.